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Instant charging

Instant charging

Submitted by Brian H on Thu, 2012-08-23 03:19

Another new battery tech, this one from Korea. Not quite "instant", but under a minute. Which, I think, would require a 5 MW source for the 85kWh battery. ;)
The Korean method takes the cathode material — standard lithium manganese oxide (LMO) in this case — and soaks it in a solution containing graphite. Then, by carbonizing the graphite-soaked LMO, the graphite turns into a dense network of conductive traces that run throughout the cathode. This new cathode is then packaged normally, with an electrolyte and graphite anode, to create the fast-charging li-ion battery. Other factors, such as the battery’s energy density and cycle life seem to remain unchanged.
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These networks of carbonized graphite effectively act like blood vessels, allowing every part of the battery to recharge at the same time — thus speeding up recharge by 30 to 120 times.

That probably also means 30 to 120 times more power output. instead of getting 300kW you get 36MW out of the 85kWh battery. Outpower top fuel dragsters by factor of six.

FriendOfGaia |
23 agosto 2012

Whats about the idea to extend the input voltage from the current maximum of 250 V to 750 V. In this way the 400 V phases or the 700 V phases in Europe could be used. While it does not increase the chargers power it would however load the power grid much more evenly there. Currently the Europeans do not allow a single-phase load, this is L to N with 230V, of more than 32 A. With 400 V or 700 V the single-phase load would turn into a two-phase load. Still not evenly, but much better for the Grid.

FriendOfGaia |
23 agosto 2012

Another subject.
I recently heard about trouble of an owner of a Tesla Roadster in Japan. He stated that the voltages are incompatible there. I have been in the United States and Japan many times. Both countries use the single phase three conducter feeder for residental and small business areas. The only difference is in Japan 100/200 V and not as in the US of 115/230 V. The frequency is, oddly, 50 Hz in the North and 60 Hz south. But this should not pose any problems.

Timo |
23 agosto 2012

Model S will have three-phase charging for European models. That's what has been promised. Probably just common 400V though.

Tesluthian |
16 ottobre 2012

Quadruple Charging Speed
If you redesign and divide the tesla battery into four separate sections, is it not possible to charge four times faster with four plugs going into four different batteries ? That's 15 seconds for Korean charger, and 7 & 1/2 minutes for the current supercharger station.

Timo |
17 ottobre 2012

No it is not possible. In fact you can't charge even single cell in that battery pack any faster than SC already does. No much faster, maybe a little if you push it. You need different battery chemistry to gain faster charging rate. Once you do have different battery chemistry that accepts higher charging currents, then it is only question of volts and amps and how to do it safely (plug used, cables etc.)

evanstumpges |
18 ottobre 2012

I don't think either Tesluthian or Timo have this quite right.

As I think Timo was trying to get at, the charging rate is limited by the individual cell, so baring the availability of new battery cell technology that can tolerate higher charging rates, it is not possible to charge the cells faster than Tesla is currently doing it.

However, Tesluthian is correct that pack design can affect the maximum battery pack charging current, which is the current that the Super Charger provides. A battery pack is built with groups of cells connected in parallel (modules) that are connected to each other in series to achieve the desired voltage. The pack charging current from the Super Charger is equal to the current passing though all of the battery modules. However, the current passing through each module is evenly distributed to each parallel connected cell within the module.

So technically, Tesluthian is correct that the pack charging speed could theoretically be quadrupled (by cutting the number of modules by a factor of four and quadrupling the number of cells in each module). However, this would result in a pack voltage that is only 1/4 of what Tesla currently uses and would be very undesirable. Higher bus voltage substantially reduces i2r power loss throughout the vehicle power lines...

I have no doubt that Tesla optimized the voltage and current of their battery packs to maximize efficiency, while still providing plenty of current for fast acceleration and reasonably fast charging...

Vawlkus |
19 ottobre 2012

Actually, I think Timo was saying the super charger won't charge 4 1/4 sized batteries any fast than it will charge 1 full sized battery owing to the fact that the charger is not being bottle necked by the size of the battery, but by how fast the cells will accept power.

evanstumpges |
19 ottobre 2012

Vawlkus, you might be right about Timo's post. He didn't make this point very clearly.

What you say is true. To charge faster, you need both of the following:
1. Different cells with higher charging capacity or a reconfigured pack with more cells per module.
2. A charger that can provide more power for charging.

Timo |
19 ottobre 2012

Vawlkus, you might be right about Timo's post. He didn't make this point very clearly.

Let's try a thought experiment, imagine four Tesla cars with imaginary 75 mile battery packs, (each battery pack 1/4 the size of a 300 mile battery pack), Each Tesla parked side by side in four separate super charger stations, each car plugged in and charging on one cord each.

For this example, let's keep the charging time constant. In 15 minutes all four cars are fully charged to run 75 miles, which is the current rate of today's supercharges. Each Tesla can go 75 miles; but all four cars together can go 300 miles total after 15 minutes of charging.

Now let's say a Teslar engineer comes along and takes out the 75 mile battery packs out of three of the cars and puts them all into the 4th Tesla keeping each battery pack separate and say one battery dedicated to supplying power to each wheel, with it's own separate charging cord plug. This modified Tesla car now has four batteries and four charging plug ports. This modified Quad-battery now has a range of 300 miles.

Next the Tesla Engineer gets some extension cords and connects four charger cords to the single Quad-battery Tesla car. This car, (when low on energy), with four charger cords plugged in will now charge in 15 minutes and go 300 miles, exactly the same as four separate 75 mile cars, would it not?

And in 10 years, if battery/supercharger efficiency doubles, could you not charge 600 miles in 15 minutes with a Quad-battery system ?

Another quick example, if you had 4 rechargeable C batteries, would you charge one at a time or all four at once? Isn't each battery is separate and charging at the same rate and receiving its own current?

Timo |
21 ottobre 2012

@Tesluthian, that four times 75mile battery pack would be 1200mile battery pack (4*300miles).

Charging rate is limited by battery chemistry. Not battery layout.

Once there is battery chemistry that allows higher charging rate (and allows as high or higher energy density with as low price as current system) I bet there will be faster supercharging stations too. If not immediately, then soon after.

curiousguy |
21 ottobre 2012

another problem is any time you read these very nice papers using nanomaterials look in the experimental sections and see the scales of materials they can generate and use. typically most of the nano stuff is NOT scalable and cannot (yet) even dream of going into any sort of large scale production.

Brian H |
21 ottobre 2012

Actually, Timo, he's not increasing cell charge rates. Just using 4 SC units at once, each charging ¼ of a battery, temporarily "isolated" during the process. Of course, the catch is those 4 charging units and charge ports!

Doubling and doubling again the SC power would only achieve the same thing if the current could be "split" at the charge port, to emulate 4 separate feeds, each going to a different segment of the battery.

Sounds unworkably complex to me.

Tesluthian |
21 ottobre 2012

Thanks for the help Brian. I especially like your description in the second paragraph. As for complex, I think someone who builds rocket ships could handle it, especially if it quadruples the charge time, it would be worth the effort. It would increase the appeal of Tesla and set it apart from other EV's by helping to reduce range anxiety and increase traveling convenience.

And remember, Tesla sells battery packs to other manufacturers, so if this is a desired, improvement, it could help those sales as well. But your right to consider complexity and design manufacturing simplicity into a quad-battery for the most efficient production. Maybe even consult an Industrial Ecologist about how much it may improve the ecology footprint compared to Ice cars and have them write a peer reviewed paper on it.

Timo |
22 ottobre 2012

@Brian H, you can't "temporarily isolate" one quarter of the battery for that charging. It just plain takes full hour to charge 1C battery full no matter how small units you use. Even if you split it 8000 times (number of individual cells in the pack).

Alex K |
22 ottobre 2012

@evanstumpges | OCTOBER 18, 2012: As I think Timo was trying to get at, the charging rate is limited by the individual cell, so baring the availability of new battery cell technology that can tolerate higher charging rates, it is not possible to charge the cells faster than Tesla is currently doing it.

Alex K and Timo;
you're still thinking of a single feed. Tesluthian is imagining a separate feed for every "section", isolated as if they were totally separate devices, like four iPads side-by-side. Are you trying to say that because four iPads are near each other, they each take 4x as long to charge, as if electrically joined at the hip?

"Isolated" may not be possible, of course.

Brian H |
22 ottobre 2012

I do understand that lower cap batteries don't take charge at the same quantitative rate as higher. But one 18650 cell doesn't take an hour to charge at max current. So perhaps there's a saw-off there.

Timo |
23 ottobre 2012

With four different batteries with four feeds you have four times the battery size. 1200mile battery instead of 300 miles. Four iPad batteries take four iPad battery size. Can't say it more clearly than that.

Alex K |
23 ottobre 2012

@Brian H | OCTOBER 22, 2012: I do understand that lower cap batteries don't take charge at the same quantitative rate as higher. But one 18650 cell doesn't take an hour to charge at max current. So perhaps there's a saw-off there.

You can see that the charge time at 40ºC is about 2.5 hours. Also the charging protocol for Li-Ion batteries is Constant Current/Constant Voltage. For the UR18650F, constant current is applied for about an hour and then the current tapers off as constant voltage is applied. Charging is much slower at lower temperatures.

In all the above parallel charging scenarios that have been postulated, the assumption is that the charge rate for 18650 batteries is very fast - in the order of 15 minutes, this is not true. The charge rate is more in the order of hours - the spec sheet actually lists 3 hrs.

Brian H |
23 ottobre 2012

Ah, so.

Tesluthian |
23 ottobre 2012

Follow up #2: Quadruple Charging Speed

"Timo ...four times the battery size." Ok that hypothesis needs some research, is the 85 kWh battery twice as big in volume, weight and material as the 40 kWh battery ? Anyone know?

To avoid confusion and simplify, let's keep to the original equation. Four separate 75 mile batteries in one Tesla car charging 15 minutes with four separate supercharger leadins will give 300 miles of charge in that 15 minute charging time. That is the original hypothesis using today's state of super charging.

Now how many kWh's would each of these batteries be in the car with four batteries? Each imaginary battery would be about 20 kWh or about 1/4 the amount of the real 85 kWh battery. So it seems to charge faster to 300 miles in 15 minutes, you only need about 80 kWh of battery divided into four 20 kWh batteries. What I believe Timo is saying is that a 4 battery system, needs to be four times bigger by weight, volume and
material to charge in 15 minutes. Now let's set up a comparison for the thesis question:

"If one of Elon's super chargers can put in 75 miles of charge to a single 85 kWh car battery in 15 minutes with a single supercharger lead in, then is it possible that 4 separate 20 kWh batteries in one Tesla car with four separate supercharger leadins will charge each battery 75 miles of charge in 15 minutes and will thus give the four battery car a total charge of 4 X 75 miles of charge = 300 miles of total charge in that 15 minutes without the four batteries together being any heavier or bigger by volume and material than one single 85 kWh battery?

Analogy: Does a AA battery charge faster than a C battery at the same charge rate ? If yes then do four AA batteries, each battery recharging in four separate rechargers and four different wall outlets, charge faster than a single C battery in a single charger using a single wall outlet ? Are the four AA batteries together about the same weight, volume and material as the C battery?

Timo |
24 ottobre 2012

It's just the battery tech used, nothing more. Those cheap, high energy density batteries Tesla is using don't allow high charge currents. That is the (main) reason SC is not even offered to 40kWh version.

There are batteries that allow much higher currents to be used, but they tend to be either a lot more expensive or have weaker energy density (or both), which means you would need bigger battery to get same range.

Battery tech will continue to develop. Soon the limit is no longer the battery itself like it is now, but the method of charging that high current safely. Four feeds in one is just matter of "what kind of plug should we use".

Something like 60C RC batteries already exist, those could be recharged in about one minute. Too expensive and a bit too weak energy density to be used in long range BEV, but we are getting there.

You don't seem to understand that the limit is not the charging current but the battery itself in Tesla cars. All batteries in the pack are charged at the same time giving you maximum charge current. SC is pretty close to max of what the battery pack can handle. Dividing that battery means that you also divide the maximum charge current IE, smaller battery allows less current giving you exactly same allowed charge time. Trying to charge smaller battery with same current as original battery would result in explosion from overcharging.

evanstumpges |
24 ottobre 2012

@Tesluthian

This comes back to my original post in this thread. Your proposed battery pack would indeed allow the car to charge 4 times as fast. However, the pack voltage would be reduced by a factor of 4. Due to greatly increased I2R current losses, running at this low a voltage would be rather inefficient (undesirable). Tesla's motor controller might not even turn on at 1/4 of the input voltage it expects.

When designing a battery pack, one of the first constraints that must be met is the overall voltage. Knowing the voltage requirement allows you to determine how many modules must be connected in series to satisfy this specification. From there, the pack capacity is set by determining how many cells will be connected in parallel for each battery module.

If you were to split Telsa's battery pack into four separate sections, there are two options. Both provide the same total energy storage (kWh) and don't affect size or weight.
1. All four batteries can be connected in parallel. This is the selection you made and it means the total voltage is now just 1/4 of the original pack, but you can charge at four times the rate (assuming your charger(s) can provide that much power)
2. All four batteries can be connected in series. This is essentially, no different from the original pack. The voltage and charging rate remain unchanged.

For any pack design, there is a tradeoff between voltage and Ah capacity. You can trade one for the other by modifying the pack (module) design but you can't increase both at the same time without fundamentally improved battery cell technology.

This is basic electrical engineering. Sorry, but you can't beat the laws of physics...

Brian H |
24 ottobre 2012

Here's the trick. Charge in parallel, then reconnect in series to drive!
;)

evanstumpges |
25 ottobre 2012

@Brian H.

Hadn't thought of that. It's an interesting idea and theoretically it should work. However, it would undoubtedly increase cost, design complexity, and efficiency would be lower due to additional relays and higher I2R losses when charging. These technical challenges are significant, but the idea could be worth exploring for future Superchargers as a way to further accelerate EV charging.

curiousguy |
20 giugno 2014

the bottleneck with charging batteries (as opposed to capacitors) is the solid state diffusion of the mobile species (Li+ cation) into the anode and especially the cathode. if the Li+ cations are jammed in the channels of the CoO2 crystal structure cathode at a rate faster than it can organize itself inside that space it just wont go in, and that results in reduced capacity. furthermore, if jammed in fast enough there will be irreversible strain on the crystal structure which will affect further cycles.

so the limit for this technology is at the chemistry level, not at the engineering level.

Brian H |
20 giugno 2014

To make the supercaps handle enough of the charge to make a difference, they get bulky.